A metal shell may have a better appearance and better texture, in addition, the metal shell may have a better wear resistance and a better scratch resistance. With a development of metal processing technology, mobile phones, tablet PCs and other mobile communication equipment, tend to use metal shell more and more. However, electromagnetic waves could not penetrate the metal shell, especially a metal shell with a large area. In order to achieve a good electrical signal effect, when a metal shell is used, one or more slits need to be processed on the metal shell, and an antenna needs to be designed in the slits.
Current method of processing the slits is mainly by using green light and other shorter wavelength laser to peel a metal substrate layer by layer. A processing efficiency of the current method is low, and due to a problem of depth of focus, a thick metal substrate could not be processed (a thickness of the metal substrate at most could reach 0.4 mm), a product obtained by such processing has low strength. In addition, the processing needs to be repeated several times to cut the metal substrate. A high-velocity scanning of galvanometer which controls a laser path has a certain accuracy, and repeated processing can reduce the processing-accuracy and extend the processing-time. Also the slits processed by this method have a large taper, that is, an outer surface (i.e., an upper surface) is larger than an inner surface (i.e., a lower surface).